This invention relates generally to gas turbine engines, and more particularly, to methods and apparatus for operating gas turbine engines.
Gas turbine engines typically include high and low pressure compressors, a combustor, and at least one turbine. The compressors compress air that is mixed with fuel and channeled to the combustor. The mixture is then ignited for generating hot combustion gases, and the combustion gases are channeled to the turbine which extracts energy from the combustion gases for powering the compressor, as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator.
Because gas turbine engines must be capable of operating in a variety of operating conditions, the engines include control systems to control fuel flow during engine operations. More specifically, the control systems compare inputs received from engine parameters, such as rotational speed of a fan, to power management schedules preloaded in the control systems.
When engines operate in hail conditions, hail may be undesirably ingested into the engine core and passed through to the combustor. Over time, continued operation of the engine with significant hail ingestion within the combustor, may cause the combustor to flame-out. More specifically, at least some known aircraft engines are susceptible to flameouts and/or rollbacks when hail is encountered and ingested at low engine power operating conditions, such as idle descent. To facilitate reducing problems associated with hail ingestion, at least some known engines include a variable bypass valve (VBV) system. VBV systems are designed to extract a substantial portion of hail ingested in an engine core and centrifuge it into the engine bypass stream. However, such VBV systems are complex, may provide only limited benefits, and may increase an overall assembly cost of the engine.
In one aspect of the invention, a method for controlling an aircraft engine using a control system is provided. The control system includes a processor coupled to the aircraft engine. The method comprises receiving a compressor discharge pressure from the aircraft engine, receiving current engine environmental operating conditions, determining a reference value for a controlled variable from a fuel flow schedule, generating a fuel-air-ratio for the reference value based on current engine environmental operating conditions, and enriching combustor fuel staging in response to the fuel-air-ratio.
In another aspect, a control system for controlling an aircraft engine is provided. The control system is coupled to the aircraft engine for receiving a plurality of reference inputs from engine sensors coupled to the engine, including at least one input indicative of engine environmental operating conditions. The control system is configured to produce a commanded fuel flow in response to engine environmental operating conditions and the engine sensor values.
In a further aspect of the invention, an aircraft engine fuel control system is provided. The system is coupled to the aircraft engine to receive reference inputs from the engine to determine a state of the aircraft engine including at least one input indicative of engine hail ingestion. The system is configured to enrich combustor fuel staging in response to engine hail ingestion and the engine sensor values.